This invention relates to a liquid jet unit used in an industrial machine, such as a manufacturing machine for manufacturing optical filters, and an image recording apparatus such as a plotter and a printer, and a piezoelectric vibrator unit used in the liquid jet unit. This invention also relates to methods of manufacturing the liquid jet unit and the piezoelectric vibrator unit.
Industrial machines such as manufacturing machines and image recording apparatuses such as plotters and printers are available, which employ a liquid jet head for ejecting liquid in the form of liquid droplets. For example, an industrial machine for manufacturing an optical filter is designed to eject color material in the form of liquid droplets onto a filter substrate using an ejection head (a kind of liquid jet head). An image recording apparatus is designed to eject ink droplets from a recording head (a kind of liquid jet head) onto a printing or recording medium such as paper.
These industrial machines and image recorders require high accuracy for the amount and speed of the ejected liquid droplets. For example, the optical filter manufacturing machine must eject a proper amount (i.e. a proper ejection amount) of an color material droplet onto a proper position with high accuracy since the optical filter manufactured with the industrial machine is used with a liquid crystal display, etc. The image recording apparatus requires high accuracy as to a position onto which an ink droplet is ejected, and an amount of the ejected ink, in order to improve image quality and speed up the recording.
The liquid jet head, widely used in these industrial machines and image recording apparatuses, typically includes: a flow passage unit formed with a plurality of ink flow passages each extending from a reservoir through a pressure chamber to a nozzle opening; and a piezoelectric vibrator unit being placed on the rear of the flow passage unit and having a plurality of piezoelectric vibrators provided in a one-to-one correspondence with the pressure chambers for changing the volumes of the corresponding pressure chambers. The liquid jet head ejects liquid from a nozzle opening by changing the volume of the corresponding pressure chamber using deformation (displacement) of the corresponding piezoelectric vibrator.
The piezoelectric vibrator unit is manufactured, for example, according to the following procedure: First, common internal electrodes and segment internal electrodes are laminated alternately with a piezoelectric material interposed between adjacent internal electrodes to manufacture a plate-like laminated substrate, and a common external electrode electrically conducted to the common internal electrodes and a segment external electrodes electrically conducted to the segment internal electrodes are formed on the surface of the laminated substrate to obtain a laminated member. After the base end side portion of the laminated member is fixed to a fixing plate, the leading end side portion of the laminated member is cut into a plurality of segments (piezoelectric vibrators) each having an extremely narrow width of about 50 μm to 100 μm using a wire saw, a dicing saw, etc.
The piezoelectric vibrator unit thus manufactured is disposed in a state in which the displaceable surfaces of piezoelectric vibrators are contacted with diaphragm parts for the pressure chambers, respectively.
Another type of the liquid jet head has piezoelectric vibrators that are provided in the diaphragm parts for the pressure chambers, respectively. The liquid jet head of this type ejects liquid from a nozzle opening by changing the volume of the corresponding pressure chamber using deformation (displacement) of the corresponding piezoelectric vibrator similarly.
The liquid jet head using the piezoelectric vibrator unit has an advantage in that piezoelectric vibrators having identical displacement characteristic can be easily obtained because the piezoelectric vibration unit is manufactured such that the laminated member is cut to provide the piezoelectric vibrators. Namely, a come-like piezoelectric vibrator is provided by cutting substantially the same piezoelectric vibrator unit. Therefore, since it is substantially the same one first, the variation in the characteristic between each piezoelectric vibrator is small. However, each piezoelectric vibrator obtained as a consequence of cutting has an extremely narrow width, and therefore slight variation in width may occur. Since the piezoelectric vibrator is of laminated type, if a pinhole larger than the width of the piezoelectric vibrator exists in the internal electrode, the internal electrode is brought partially out of electric conduction by the presence of the pinhole. In the case of the industrial machine of which especially high precision is required, even if it is the small piezoelectric vibrator of variation, the small highly precise characteristic of variation is demanded more than it. Thus, the width variation of the piezoelectric vibrators, the defect of the internal electrode, and the like cause the piezoelectric vibrators to have sight varied displacement amounts.
In the case of the liquid jet head in which the piezoelectric vibrators are provided in the diaphragm parts for the pressure chambers, the thickness, shape, etc., of piezoelectric material is likely to be varied, and thus the displacement amounts of the piezoelectric vibrators are varied largely in comparison to the case where the piezoelectric vibrators constitute the piezoelectric vibrator unit.
Such displacement amount variation of the piezoelectric vibrators adversely affect the liquid ejection characteristic of the liquid jet head and thus is not preferable. For example, in the case of the optical filter manufacturing machine, the sizes of pixels forming the optical filter are varied depending on the respective nozzle openings, and in the case of the image recording apparatus, the pixels deposited onto a recording medium are made non-uniform in size.
Further, the liquid ejection characteristic of the liquid jet head is also changed due to the attachment state of the vibrator unit to the flow passage unit and the shape of the ink flow passage in the flow passage unit.
To prevent these problems, it is conceivable to fill one scanning line with liquid droplets ejected from a plurality of nozzle openings, but this will lower the throughput since the liquid jet head needs to be scanned plural times to fill one scanning line.
This is particularly not preferable for the industrial machines since the lowered throughput results in lowered production efficiency and thus increased cost of the product.